Interface Barrier Energy Determination from Voltage Dependence of Photoinjected Currents
01 May 1970-Journal of Applied Physics (American Institute of Physics)-Vol. 41, Iss: 6, pp 2424-2432
TL;DR: In this paper, a theoretical analysis of the dependence of photocurrent on voltage and photon energy is presented, and it is shown that barrier heights are obtainable by examination of the V•I characteristics to determine the sign of the second derivative.
Abstract: Interface barrier energies and their dependence on applied field may be obtained from the voltage dependence of currents produced by electron photoinjection from an electrode. Unlike the conventional Fowler plot method, direct measurement is possible and knowledge of the absorbed light intensity is not required. A theoretical analysis gives the dependence of photocurrent on voltage and photon energy, and it is shown that barrier heights are obtainable by examination of the V‐I characteristics to determine the sign of the second derivative. Theoretical forms of the V‐I characteristics are derived for specific electron energy distributions which should be generally applicable. Experimental results from MIS structures using thermally grown SiO2 on degenerate n‐type silicon are found to be in good agreement with theoretical predictions. Thresholds for emission from the conduction band (3.2 eV) and from the valence band (4.16 eV) are clearly defined in the V‐I characteristics. The fact that the difference betw...
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TL;DR: A new architecture based on surface plasmon excitation within a metal-insulator-metal device that produces power based on spatial confinement of electron excitation through plAsmon absorption is shown.
Abstract: Conversion of light into direct current is important for applications ranging from energy conversion to photodetection, yet often challenging over broad photon frequencies. Here we show a new architecture based on surface plasmon excitation within a metal–insulator–metal device that produces power based on spatial confinement of electron excitation through plasmon absorption. Plasmons excited in the upper metal are absorbed, creating a high concentration of hot electrons which can inject above or tunnel through the thin insulating barrier, producing current. The theoretical power conversion efficiency enhancement achieved can be almost 40 times larger than that of direct illumination while utilizing a broad spectrum of IR to visible wavelengths. Here we present both theoretical estimates of the power conversion efficiency and experimental device measurements, which show clear rectification and power conversion behavior.
285 citations
TL;DR: In this article, the authors give an overview of the challenges and issues pertaining to high-κ gate dielectric-based devices, including flat-band and threshold voltage control, carrier mobility degradation, charge trapping, gate wear-out and breakdown, and bias temperature instabilities.
Abstract: High- κ gate dielectrics like HfO 2 and HfSiO(N) are considered for the replacement of SiO 2 and SiON layers in advanced complementary metal–oxide–semiconductor (MOS) devices. Using these gate oxides allows indeed to drastically reduce the leakage current flowing through the device, as required by the specifications of the International Technology Roadmap for Semiconductors. However, major problems remain to be solved before the possible use of high- κ gate dielectrics in integrated circuits. The purpose of this paper is to give an overview of the challenges and issues pertaining to high- κ -based devices. Several issues are discussed in detail, like flat-band and threshold voltage control, carrier mobility degradation, charge trapping, gate dielectric wear-out and breakdown, and bias temperature instabilities. Our current understanding of these issues is presented, with an emphasis on the relationship between the material properties of the gate stack, and the electrical properties of the devices. The combination of metal gates with high- κ gate dielectric appears to be a promising solution for the further scaling down of CMOS devices.
251 citations
TL;DR: In this paper, the spectral onset of electron/hole photoemission from one solid into another was measured by measuring the spectral start of electron states at interfaces of insulators with metals and semiconductors.
Abstract: Internal photoemission spectroscopy provides the most straightforward way to characterize the relative energies of electron states at interfaces of insulators with metals and semiconductors by measuring the spectral onset of electron/hole photoemission from one solid into another. The article reviews the application of this technique for characterization of advanced nanometer-thin insulators prospected to be used in microelectronic devices. Fundamental aspects and technical features of the internal photoemission experiments are discussed together with basic electronic properties of a number of investigated high-permittivity insulating films and their interfaces in semiconductor heterostructures. Significant differences are found in the electronic properties of nanometer-thin amorphous insulating layers as compared to the known bulk phase characteristics. The band alignment at the interfaces of these insulators with metals is found to be highly sensitive to the surface preparation procedures. By contrast, ...
236 citations
TL;DR: The findings reveal that the semiconductor 2H-MoS2 exhibits both n- and p-type behavior, and the work function as measured by the Kelvin probe is found to vary from 4.4 to 5.3 eV, which will have to be controlled during crystal growth in order to provide high quality uniform materials for future device fabrication.
Abstract: Room temperature X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICPMS), high resolution Rutherford backscattering spectrometry (HR-RBS), Kelvin probe method, and scanning tunneling microscopy (STM) are employed to study the properties of a freshly exfoliated surface of geological MoS2 crystals. Our findings reveal that the semiconductor 2H-MoS2 exhibits both n- and p-type behavior, and the work function as measured by the Kelvin probe is found to vary from 4.4 to 5.3 eV. The presence of impurities in parts-per-million (ppm) and a surface defect density of up to 8% of the total area could explain the variation of the Fermi level position. High resolution RBS data also show a large variation in the MoSx composition (1.8 < x < 2.05) at the surface. Thus, the variation in the conductivity, the work function, and stoichiometry across small areas of MoS2 will have to be controlled during crystal growth in order to provide high quality uniform materials for future device fa...
235 citations
TL;DR: In this article, the effect of optically induced hot electron injection in MOS transistor structures to study electron traps in SiO2 films is described, by simultaneously monitoring the gate current and the surface channel conductance shift, information on the trapping efficiency, the capture cross sections, and the trap concentrations could be obtained.
Abstract: An experiment using the effect of optically induced hot‐electron injection in MOS transistor structures to study electron traps in SiO2 films is described. By simultaneously monitoring the gate current and the surface channel conductance shift, information on the trapping efficiency, the capture cross sections, and the trap concentrations could be obtained. Trap centers with capture cross sections differing by more than two orders of magnitude could probably be separated and their cross sections determined depending on their concentrations. Experimental results are presented for electron traps using n ‐channel silicon‐gate structures, with SiO2 layers thermally grown in dry oxygen. Two electron‐capture cross sections of 3.3 × 10−13 and 2.4 × 10−19 cm2 were measured. Although there was evidence indicating the presence of other electron traps their capture cross sections could not be unambiguously determined. The injection current can be described by Schottky‐emission processes at an effective electron temp...
214 citations
References
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TL;DR: In this paper, an elementary theory for the effect of temperature on the photoelectric sensitivity of a clean metal near the threshold is developed, which is in agreement with the conclusions of Lawrence and Linford based on much less extensive data.
Abstract: An elementary theory is developed for the effect of temperature on the photoelectric sensitivity of a clean metal near the threshold. It is shown that the results observed by various workers for silver, gold, tantalum, tin, and potassium can be fairly completely accounted for by the effect of the temperature on the number of electrons available for extraction according to the distribution law of Sommerfeld's theory of metals. This is in agreement with the conclusions of Lawrence and Linford based on much less extensive data. A graphical method is given enabling the whole of the observed curves near the threshold for all temperatures to be used in determining the threshold itself thus avoiding an arbitrary extrapolation to zero current. At present the fundamental theory of the effect survives in two forms, both of which are used as alternatives here, with nearly equal success. Until one or the other can be eliminated it is not possible to determine thresholds closer than about 1 percent.
1,180 citations
TL;DR: Theoretical expressions for the quantum yield and for the energy distribution of photoelectrons assuming bulk photoemission from a solid are derived in this paper, where the effects of electrons which escape without inelastic scattering after optical excitation, and of those electrons that escape after one inelastically-scattering event, are considered.
Abstract: Theoretical expressions are derived for the quantum yield and for the energy distribution of photoelectrons assuming bulk photoemission from a solid. The effects of electrons which escape without inelastic scattering after optical excitation, and of those electrons which escape after one inelastic-scattering event, are considered. The expressions relate optical transition probabilities, optical constants, and mean free paths for inelastic scattering in a solid to quantities which can be measured in photoemission experiments. Examples of photoemission data are interpreted to show how the contribution of once-scattered electrons can be separated from the contribution of those electrons which have not suffered an inelastic-scattering event before escaping. The contribution to photoemission of those electrons which have not been scattered is analyzed to show the way in which direct and nondirect optical transitions can be identified and the way in which the density of states in a solid can be determined. The contribution of once-scattered electrons to photoemission is analyzed to show the way in which the nature and strength of inelastic-scattering mechanisms can be determined. The effects of electron-electron scattering, scattering by plasmon creation, and the Auger process are described, and methods of obtaining mean free paths and other scattering parameters are suggested.
673 citations
TL;DR: In this article, the reflectance of a single crystal silicon was measured in the range 1 to 11.3 ev and the phase of the phase was computed using the Kramers-Kronig relation between the real and imaginary parts of the complex function.
Abstract: The reflectance, ${|r(\ensuremath{\lambda})|}^{2}$, of single crystal silicon was measured in the range 1 to 11.3 ev. The phase, $\ensuremath{\theta}(\ensuremath{\lambda})$, was computed from these data using the Kramers-Kronig relation between the real and imaginary parts of the complex function $\mathrm{ln}r=\mathrm{ln}|r|+i\ensuremath{\theta}$. The optical constants, $n$ and $k$, were then determined from the Fresnel reflectivity equation. The real part of the refractive index, $n$, shows a sharp maximum of magnitude 6.9 at 3.3 ev. The extinction coefficient, $k$, shows maxima of magnitude 3.1 at 3.5 ev and 5.1 at 4.3 ev; optical absorption above 3 ev is associated with the onset of strong direct transitions. The results indicate that much useful information, applicable to band structure calculations for both silicon and germanium, could be obtained from limited reflectance studies (2 to 5 ev) on Ge-Si alloys.
456 citations
TL;DR: In this article, the position of the Fermi level at a metal-semiconductor interface relative to the conduction band has been found to be a constant fraction of the semiconductor band gap for all but 3 of the 14 group IV or III-V semiconductors studied.
Abstract: The position of the Fermi level at a metal-semiconductor interface relative to the conduction band has been found to be a constant fraction of the semiconductor band gap for all but 3 of the 14 group IV or III-V semiconductors studied. In all cases, the position was essentially independent of the metal work function. This general result is not inconsistent with the limited theories of surface state energies now available. The three exceptional cases can be understood in terms of a first-order perturbation to the surface state energies correlated with a similar perturbation observed in the energy gap at the (111) zone edge. Experiments are also reported on Ga(As-P) alloys, and two II-VI materials showing distinctly different behavior.
398 citations
TL;DR: In this article, a detailed calculation of the energy bands of germanium and silicon has been performed by use of the pseudopotential method, and the first three potential coefficients have been determined empirically, and all higher ones set equal to zero.
Abstract: A detailed calculation of the energy bands of germanium and silicon has been performed by use of the pseudopotential method. The first three potential coefficients have been determined empirically, and all higher ones set equal to zero. This potential was used to compute the energy eigenvalues at \ensuremath{\sim}50 000 points throughout the Brillouin zone. By use of this sample, we calculated the imaginary part of the dielectric constant in the optical and near ultraviolet where direct transitions between the valence and low-lying conduction bands dominate the response. Photoelectric yield curves were obtained for comparison with recent experiments. In all cases agreement of theory and experiment was reasonable. Energy contours were constructed in several of the principal symmetry planes. These were used to explain the structure in the optical properties of Ge and Si in terms of transitions near certain important critical points. Effective masses and the static dielectric constant were also computed.
251 citations